We present simultaneous observations of energetic particles by ISEE 1 in the near-earth geomagnetic tail and by ISEE 3 in the distant geomagnetic tail following the onset of a major substorn as indicated by ground magnetograms and synchronous orbit particle data. At substorm onset, both spacecraft are in the tail lobes. About 8 min after onset, ISEE 1 enters the plasma sheet; at the plasma sheet boundary, earthward directed ion beams are observed. At the same time (within the 128-s time resolution) tailward directed ion and electron beams are observed at ISEE 3. These beams persist intermittently for 25 min. The observations are explained in terms of the substorm neutral line model, wherein the near-earth and distant plasma sheet are disconnected after reconnection has proceeded to the last closed field line within the plasma sheet. Electron plasma and magnetic field data on ISEE 3 show that during the whole time period, ISEE 3 stays in the distant lobe and does not enter the plasma sheet. The plasmoid, expected to be released after reconnection has proceeded to the lobe field, is sensed by ISEE 3 as traveling compression region. The velocity dispersion effects during the appearance and disappearance of the beams indicate that these beams are not due to temporal effects but due to crossing of layers with particles of different velocity emitted from a steady source. From the observation of gradient anisotropy effects in the high energy protons, the spacing of the layers of particles with different velocity can be derived. This allows determination of the maximum electric potential along the new neutral line. The corresponding electric field is considerably smaller than the energy of the highest energy particles observed. It is argued that the plasma sheet close to the substorm-generated neutral line contains high fluxes of high-energy particles that may be sufficient to produce the high-energy boundary layer around plasmoids. Acceleration of the high energy particles may mainly occur during substorm recovery.